/*
 * Instantiator.java April 2009
 *
 * Copyright (C) 2009, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package wx.xml.simpleframework.xml.core;

import java.util.List;

import static wx.xml.simpleframework.xml.core.Support.isAssignable;

/**
 * The <code>Instantiator</code> object is used to represent an single
 * constructor within an object. It contains the actual constructor
 * as well as the list of parameters. Each instantiator will score its
 * weight when given a <code>Criteria</code> object. This allows
 * the deserialization process to find the most suitable one to
 * use when instantiating an object.
 *
 * @author Niall Gallagher
 */
class SignatureCreator implements Creator {

    /**
     * This is the list of parameters in the order of declaration.
     */
    private final List<Parameter> list;

    /**
     * This is the map that contains the parameters to be used.
     */
    private final Signature signature;

    /**
     * This is the type represented by the creator instance.
     */
    private final Class type;

    /**
     * Constructor for the <code>Instantiator</code> object. This is used
     * to create a factory like object used for instantiating objects.
     * Each instantiator will score its suitability using the parameters
     * it is provided.
     *
     * @param signature this is the signature that contains parameters
     */
    public SignatureCreator(Signature signature) {
        this.type = signature.getType();
        this.list = signature.getAll();
        this.signature = signature;
    }

    /**
     * This is the type associated with the <code>Creator</code> object.
     * All instances returned from this creator will be of this type.
     *
     * @return this returns the type associated with this creator
     */
    public Class getType() {
        return type;
    }

    /**
     * This is the signature associated with the creator. The signature
     * contains all the parameters associated with the creator as well
     * as the constructor that this represents. Exposing the signature
     * allows the creator to be validated.
     *
     * @return this is the signature associated with the creator
     */
    public Signature getSignature() {
        return signature;
    }

    /**
     * This is used to instantiate the object using the default no
     * argument constructor. If for some reason the object can not be
     * instantiated then this will throw an exception with the reason.
     *
     * @return this returns the object that has been instantiated
     */
    public Object getInstance() throws Exception {
        return signature.create();
    }

    /**
     * This is used to instantiate the object using a constructor that
     * takes deserialized objects as arguments. The object that have
     * been deserialized can be taken from the <code>Criteria</code>
     * object which contains the deserialized values.
     *
     * @param criteria this contains the criteria to be used
     * @return this returns the object that has been instantiated
     */
    public Object getInstance(Criteria criteria) throws Exception {
        Object[] values = list.toArray();

        for (int i = 0; i < list.size(); i++) {
            values[i] = getVariable(criteria, i);
        }
        return signature.create(values);
    }

    /**
     * This is used to acquire a variable from the criteria provided.
     * In order to match the constructor correctly this will check to
     * see if the if the parameter is required. If it is required then
     * there must be a non null value or an exception is thrown.
     *
     * @param criteria this is used to acquire the parameter value
     * @param index    this is the index to acquire the value for
     * @return the value associated with the specified parameter
     */
    private Object getVariable(Criteria criteria, int index) throws Exception {
        Parameter parameter = list.get(index);
        Object    key       = parameter.getKey();
        Variable  variable  = criteria.remove(key);

        if (variable != null) {
            return variable.getValue();
        }
        return null;
    }

    /**
     * This is used to score this <code>Instantiator</code> object so that
     * it can be weighed amongst other constructors. The instantiator that
     * scores the highest is the one that is used for instantiation.
     * <p>
     * If any read only element or attribute is not a parameter in
     * the constructor then the constructor is discounted. This is
     * because there is no way to set the read only entity without a
     * constructor injection in to the instantiated object.
     *
     * @param criteria this contains the criteria to be used
     * @return this returns the score based on the criteria provided
     */
    public double getScore(Criteria criteria) throws Exception {
        Signature match = signature.copy();

        for (Object key : criteria) {
            Parameter parameter = match.get(key);
            Variable  label     = criteria.get(key);
            Contact   contact   = label.getContact();

            if (parameter != null) {
                Object value  = label.getValue();
                Class  expect = value.getClass();
                Class  actual = parameter.getType();

                if (!isAssignable(expect, actual)) {
                    return -1.0;
                }
            }
            if (contact.isReadOnly()) {
                if (parameter == null) {
                    return -1.0;
                }
            }
        }
        return getPercentage(criteria);
    }

    /**
     * This is used to determine what percentage of available values
     * can be injected in to a constructor. Calculating the percentage
     * in this manner ensures that the best possible fit will be used
     * to construct the object. This also allows the object to define
     * what defaults it wishes to set for the values.
     * <p>
     * This will use a slight adjustment to ensure that if there are
     * many constructors with a 100% match on parameters, the one
     * with the most values to be injected wins. This ensures the
     * most desirable constructor is chosen each time.
     *
     * @param criteria this is the criteria object containing values
     * @return this returns the percentage match for the values
     */
    private double getPercentage(Criteria criteria) throws Exception {
        double score = 0.0;

        for (Parameter value : list) {
            Object key   = value.getKey();
            Label  label = criteria.get(key);

            if (label == null) {
                if (value.isRequired()) {
                    return -1;
                }
                if (value.isPrimitive()) {
                    return -1;
                }
            } else {
                score++;
            }
        }
        return getAdjustment(score);
    }

    /**
     * This will use a slight adjustment to ensure that if there are
     * many constructors with a 100% match on parameters, the one
     * with the most values to be injected wins. This ensures the
     * most desirable constructor is chosen each time.
     *
     * @param score this is the score from the parameter matching
     * @return an adjusted score to account for the signature size
     */
    private double getAdjustment(double score) {
        double adjustment = list.size() / 1000.0;

        if (score > 0) {
            return adjustment + score / list.size();
        }
        return score / list.size();
    }

    /**
     * This is used to acquire a descriptive name for the instantiator.
     * Providing a name is useful in debugging and when exceptions are
     * thrown as it describes the constructor the instantiator represents.
     *
     * @return this returns the name of the constructor to be used
     */
    public String toString() {
        return signature.toString();
    }
}